1. Field of the Invention
The present invention relates to a method for manufacturing semiconductor substrates each having an SOI (silicon on insulator) structure in which a semiconductor layer is provided on an insulating surface and a method for manufacturing semiconductor devices each having an SOI structure.
2. Description of the Related Art
In recent years, development of electric appliances and electronic devices has not been stopped and higher-speed semiconductor devices have been demanded. Further, with development of portable devices and increasing of energy demand, decreasing of power consumption is also one big development theme. Due to such a background, as compared to a semiconductor device manufactured using a bulk silicon substrate, an SOI technology capable of providing a high-speed, low-power-consumption semiconductor device has attracted attention. The SOI technology is a technology in which a substrate having a structure in which a thin semiconductor layer is provided over an insulator is manufactured and a semiconductor device is provided using the substrate. The semiconductor device manufactured according to the SOI technology has characteristics in that, for example, parasitic capacitance between a drain and a substrate of a transistor is small and a leakage current into the substrate is small. Furthermore, when the SOI technology is used, a semiconductor layer used for an active layer of a transistor can be thinned, so that a completely-depleted transistor can be manufactured, and further high performance can be achieved.
Further, the semiconductor device manufactured using such a substrate also has a characteristic in that a short-channel effect can be effectively suppressed to be able to realize high-density integration, and characteristics in that circuit breakdown (i.e., latch-up) due to parasitic thyristor, that is a capital problem in a semiconductor device manufactured using a bulk silicon substrate, and against which, various measures such as circuit design have been taken, does not occur in principle.
As a method for manufacturing a semiconductor substrate having an SOI structure, a hydrogen-ion-implantation separation method is known (e.g., see Japanese Published Patent Application No. 2000-124092). According to the hydrogen-ion-implantation separation method, hydrogen ions are implanted into a silicon wafer provided with an oxide film on the surface, to form a microbubble layer at a given depth from the surface, and a silicon layer with a desired thickness is bonded to a silicon wafer by using the microbubble layer as a cleavage plane. In this method, it is necessary to perform, in addition to thermal treatment for separation at a temperature equal to or higher than 500° C., thermal treatment at a temperature of 1000° C. to 1300° C. under an inert gas atmosphere in order to increase the bonding strength.
On the other hand, a semiconductor device in which a silicon layer is formed over an insulating substrate such as a high-heat-resistant glass substrate is disclosed (e.g., Japanese Published Patent Application No. H11-163363). The semiconductor device has a structure in which an entire surface of crystallized glass, a strain point of which is equal to or greater than 750° C., is protected by an insulating silicon film and the silicon layer obtained by the hydrogen-ion-implantation separation method is firmly fixed over the insulating silicon film.